In a hip joint replacement surgery, an artificial femoral prosthesis is implanted into a patient's femur for completing the surgery.
A conventional femoral stem 50 as shown in FIG. 1 is provided or served for such an artificial femoral prosthesis. The femoral stem 50 is integrally formed by metallic materials and is tapered downwardly adapted to be inserted into a medullary cavity 41 in a patient's femur 40. A centering retainer 51 is jacketed on a bottom tip of the femoral stem 50. Before inserting the femoral stem 50 into the medullary cavity 41 of the femur 40, a fixation agent P such as bone cement is filled into the medullary cavity 41. Upon insertion of the femoral stem 50 into the medullary cavity 41, the femoral stem 50 will be suspended within the fixation agent P. By the aid of centering retainer 51, the stem 50 will then be automatically positioned in the central position of the medullary cavity 41. After the fixation agent P is cured, the femoral stem 50 will be stably implanted in the medullary cavity 41 of the femur 40.
After the fixation agent P is cured, the hardened fixation agent P will lose its buffer effect. So, any external impact force acting upon the femoral stem 50 will be directly transferred to the femur 40, without being diffused or dampened. As shown in FIG. 2, if the external force F acts on the top portion of the stem 50, a bending moment M will exert on the stem 50 to thereby bias the femur 40 to possibly cause fracture of the femur 40 or stem 50, resulting in a failure of the hip joint replacement surgery.
It is therefore expected to design or create a femoral implant having a buffer mechanism provided therein so as to dampen any external force acting thereupon for a safe protection of the femoral implant and femur.